1. Field of the Invention
The present invention relates to a sheet treating apparatus, and more particularly, it relates to a sheet treating apparatus used with an image forming apparatus such as a copying machine, a laser beam printer and the like and having a first treating means (referred to as "treating tray" hereinafter) for effecting treatment such as stapling or sorting sheets discharged from the image forming apparatus and a second treating means (referred to as "stack tray" hereinafter).
2. Related Background Art
In the past, various techniques regarding a combination of a treating tray for stapling a sheet bundle if desired and a stack tray for receiving each sheet bundle and for containing the sheet bundle have been proposed as disclosed in Japanese Patent Application Laid-open No. 2-144370. FIG. 27 is a sectional view showing an example of such a technique.
In FIG. 27, the reference numeral 501 denotes a treating tray; and 502 denotes a stack tray. Around the treating tray 501, there are provided a stapler 503 for effecting stapling, and a jogger 504 for effecting alignment of sheets while shifting frontward and rearward.
With the above-mentioned arrangement, a sheet bundle aligned on the treating tray (staple tray) and stapled is discharged onto the stack tray 502 by a pair of bundle discharge rollers 505, 506. In order to sort the sheet bundles discharged onto the stack tray 502, the stack tray 502 can be shifted frontward and rearward (in a direction of the width of the sheet) for each sheet bundle and can be shifted upward and downward to align the surface of the sheet bundle with the bundle discharge roller pair, so that the stack tray 502 is lowered while sorting the sheets frontward and rearwawrd.
Both the treating tray 501 and the stack tray 502 are inclined so that downstream (left) ends thereof are located higher than upstream ends thereof, and trailing ends of the sheets on the stack tray 502 are regulated by a rear end wall 507.
Incidentally, the reference numerals used in the conventional technique shown in FIG. 27 do not relate to the reference numerals used in the present invention.
However, in the above-mentioned conventional technique, as the sheet bundles are successively discharged, when a larger number of sheets (about 1000 sheets or more) are stacked on the stack tray 502, lower sheets are contacted with the rear end wall 507 with great pressure due to the weight of the upper sheets. In this condition, when the stack tray 502 tries to be shifted frontward and rearward, rear ends of the lower sheets will be damaged or folded by significantly rubbing against the rear end wall 507.
Also, as the stack tray 502 has to be shifted frontward and rearward while resting a large number of sheets thereon, a large motor is required for shifting the stack tray 502 and a secure shifting mechanism is required.
Further, when the stack tray 502 is shifted in a condition that non-stapled sheets are stacked on the tray, if the stacking condition is unstable due to curl in the sheets or the like, the shifting movement of the is tray may cause misalignment of the sheets.